1. Field of the Invention
The present invention relates to a vehicular air conditioning apparatus which includes a cooling storage evaporator unit for cooling a cooling storage unit such as a refrigerator, a cooling storage medium and the like.
2. Description of Related Art
As one example of a vehicular air conditioning apparatus that is mounted on trucks or the like, a prior application of the applicant, Japanese Patent Laid-Open Publication No. Sho-62-149509, discloses a vehicular air conditioning apparatus which includes a main evaporator for cooling a passenger compartment and a cooling storage evaporator for cooling a cooling storage medium. In this air conditioning apparatus, the cooling storage medium cools a sleeping compartment of the truck or the like even when the engine is at a stop.
FIG. 12 shows the construction of a refrigerating cycle of the aforementioned air conditioning apparatus. As shown in FIG. 12, this air conditioning apparatus includes a compressor 1, a condenser 2, a receiver 3, a temperature expansion valve 4 and a main evaporator 5, all of which are connected by a refrigerant line 6 that forms a closed loop. The air conditioning apparatus further includes a constant pressure valve 7, a cooling storage evaporator 8 and a check valve 9, which are all provided in parallel with the temperature expansion valve 4 and the main evaporator 5. The cooling storage evaporator 8 includes an evaporator pipe that has a zigzag shape and cooling storage medium packs coupled to the evaporator pipe. The air conditioning apparatus additionally includes a solenoid valve 11 provided between a line branch point 10 and the temperature expansion valve 4, and a second solenoid valve 12 provided between the line branch point 10 and the constant pressure valve 7.
When an air conditioning switch and a cooling storage switch are both actuated, a controller (not shown) performs FIR (Freezing by Intermittent Running) control to alternately actuate the first solenoid valve 11 and the second solenoid valve 12 based on a predetermined time ratio (for example, 60 seconds for actuating the first solenoid valve 11:15 seconds for actuating the second solenoid valve 12) so that the cooling storage medium is also cooled while cooling the passenger compartment. When the cooling operation of the cooling storage medium is finished, the second solenoid valve 12 is deactuated, and the supply of refrigerant to the cooling storage evaporator 8 is terminated. Then, when the sleeping compartment switch is actuated, the sleeping compartment is cooled by the latent heat of melting of the cooling storage medium.
With the above-described air conditioning apparatus, the sleeping compartment can be cooled even if the engine is turned off and thus, this air conditioning apparatus promotes the conservation of energy and contributes to the lessening of noise and air pollution. However, according to research performed by the inventors of the present invention, the aforementioned air conditioning apparatus that is equipped with the cooling storage evaporator 8 still needs to be improved.
That is, after the cooling storage evaporator 8 completes the cooling operation of the cooling storage medium, the second solenoid valve 12 is deactuated and thus, the supply of refrigerant to the cooling storage evaporator 8 stops. Here, while the cooling storage medium of the cooling storage evaporator 8 remains frozen, the refrigerant pressure at the outlet of the cooling storage evaporator 8 will remain at a low level (for example, 0.5 kg/cm.sup.2 abs) and will be significantly lesser than the refrigerant pressure at the outlet of the main evaporator 5 (which has a pressure of, for example, 2.0 kg/cm.sup.2 abs). In this way, refrigerant at the outlet side of the main evaporator 5 will not flow back to the outlet side of the cooling storage evaporator 8 via the check valve 9.
However, when the cooling storage medium of the cooling storage evaporator 8 begins to melt, the refrigerant pressure inside the cooling storage evaporator 8 rises and thus, the refrigerant pressure at the outlet of the same cooling storage evaporator 8 also rises. As a result, the difference in pressures between the inlet and the outlet sides of the check valve 9 decreases. Thus, as shown in FIG. 13, with lesser pressure difference between the inlet and the outlet sides of the check valve 9, the amount of refrigerant flowing back (that is, leaking) from the outlet side of the main evaporator 5 to the outlet side of the cooling storage evaporator 8 via the check valve 9 begins to gradually increase. Accordingly, the amount of refrigerant that tends to remain inside the cooling storage evaporator 8 will increase, thus leading to reduced refrigerating capacity of the main evaporator 5.